The idea is to have a single macro which lets you reflect multiple
implementations. That's provided in this commit. However, there
is a hitch with implementations that have no dependencies: the
reflectedType property did not exist on the Signature type. However,
if you add it, then the Signature type becomes opaque, so we would
have to look up signatures; but that appears to be tricky, as there
doesn't seem to be a way to reflect the full generic type of the
Signatures interface.
So this commit provides three example resolutions:
(A) Export a type RTT and all no-dependency implementations have to
intersect with RTT (see 'add' in number/arithmetic.ts)
(B) Write no-dependency implementations as functions of no arguments
(representing no dependencies passed in) returning the actual
implementation (see 'subtract' in number/arithmetic.ts)
(C) Make a special DSignature<> generic type (short for "Direct Signature"
used only (and always) for implementations with no dependencies, and
a matching $Dreflect!() macro for generating their type info.
Of course, there may be other possibilities I haven't thought of. But we
need to pick one. I don't think it matters _too_ much, since there only
a small fraction of all implementations have no dependencies.
